Optical counterpart and environment of a ULX in NGC 5474

Ultraluminous X-ray sources (ULX) are non-nuclear point-like sources in external galaxies with L_{X} = 10^{39}-10^{41} erg s^{-1}. The true nature of ULXs is still not clear and multiwavelength studies allow us to understand their physical mechanisms. In this work, the optical counterpart of the ULX in NGC 5474 is found by carefully comparing the Chandra and HST WFPC2 images. The counterpart have magnitudes of 24.6 and 24.1 in F606W and F814W filters, respectively. The optical spectrum also has been obtained with 6-m BTA Telescope at Special Astrophysical Observatory (SAO, Russia) to examine the environment of the source. We discuss several options to understand the nature of the ULX.